This research project is addressed to the question of how the visceral arches develop and how they contribute to the morphogenesis of the oro-facial complex. A basic aspect of the approach to this question is to compare and contrast the development of the embryonic landscape in the mouse and in an infrahuman primate under laboratory conditions wherein development time and specimen preparation are strictly controlled. Scanning electron microscopy with microdissection within the microscope in conjunction with transmission electron and light microscopy will provide surface and subsurface details of changing contours and cell differentiation. Analysis of how three-dimensional shape changes with time will reveal differences and similarities between species at comparable stages of embryonic development. Parallel studies of the development of the chondrocranium will entail reconstruction from superimposed serial sections.